Universal Serial Bus (USB) is a cable bus that supports data exchange between a host computer and multiple simultaneously accessible peripherals. In the USB architecture a hub may, among other things, store and forward packets being transferred between a host and a device. The throughput or transfer rate of information transferred between the host and the device may be influenced by the rate at which the information is signaled by communication interfaces associated with the host, the hub, and the device.
The USB 2.0 specification (Hewlett Packard Company, et al., USB 2.0 Specification, rev. 2 (2000)) defines a nominal signaling rate of 480 Mbps, which the USB 2.0 specification refers to as a “High Speed” transfer rate. On the other hand, the USB 3.0 specification (Hewlett Packard Company, et al., USB 3.0 Specification, rev. 1 (2008)) defines a nominal signaling rate of 5 Gbps, which the USB 3.0 specification refers to as a “SuperSpeed” transfer rate. In practice, actual USB 2.0 and SuperSpeed signaling rates are typically less than the nominal USB 2.0 and SuperSpeed signaling rates.
A USB 3.0 hub is a logical combination of a SuperSpeed hub and a USB 2.0 hub. The SuperSpeed hub portion of a USB 3.0 hub is involved with the transfer of SuperSpeed packets between a host and USB 3.0 devices. The USB 2.0 hub portion of a USB 3.0 hub is involved with the transfer of USB 2.0 packets between the host and USB 2.0 devices. Depending on a number of USB 3.0 devices connected with the host through the USB 3.0 hub, SuperSpeed transfer rate capabilities between the USB 3.0 hub and the USB 3.0 host may be left underutilized.